In the making of microelectronic devices, such as semiconductor wafers, processing apparatus are frequently used to clean or otherwise process a surface of a substrate (e.g. a semiconductor wafer). Semiconductor wafers and other microelectronic devices are typically very sensitive to moisture and other contaminants. For example, semiconductor wafers typically include features such as a circuit that are comparable in size to a contaminant particle. It is thus important to prevent moisture and other contaminants from entering the processing apparatus or any other environment in which a microelectronic device is stored and/or processed.
To provide for specific processing characteristics, the processing of the wafer within a specific apparatus is often performed under evacuated conditions wherein the environment of the chamber in which the wafer is processed is held at a pressure that is less than the pressure of the environment surrounding the apparatus. For example, an aerosol cleaning apparatus can be used to clean a surface of a semiconductor wafer by impinging a stream of cryogenic fluid against the surface of the wafer. Cryogenic fluid comprises an aerosol spray including carrier gas and frozen particles, the frozen particles made by quickly freezing aerosol droplets that are created from a gas, such as argon. The flow of cryogenic fluid is propelled from a nozzle positioned over the wafer, and the frozen particles impinge upon the surface of the wafer to dislodge contaminants from the surface of the wafer. The pressure of the chamber in which the wafer is cleaned is controlled to provide a flow of cryogenic fluids that has the desired physical properties. For example, as is known, processing at a chamber pressure that is below the triple point of the cryogenic fluid that is dispensed from the cleaning nozzle will ensure the effective creation of frozen particles and thus prevent liquid cryogen droplets from falling on the workpiece, and upon evaporation leaving residues from particles originally embedded in the liquid droplet. In other words, the chamber pressure is controlled to optimize the processing steps performed within the chamber. In the case of an aerosol processing apparatus, the chamber pressure is typically controlled to be below the pressure of the environment that surrounds the apparatus. An aerosol processing apparatus for the controlled processing of a semiconductor wafer is described in U.S. Pat. No. 5,810,942, entitled "Aerodynamic Aerosol Chamber" and assigned to the assignee of the present application, the entire disclosure of which is incorporated by reference herein for all purposes.
In such an apparatus where the processing of a microelectronic device occurs at a pressure that is below the pressure of the surrounding environment, it can be difficult to control (i.e. prevent) the introduction of moisture or other contaminants into the processing chamber during transfer of the microelectronic device into or out of the processing chamber. Simply opening the processing chamber while the chamber is at the reduced pressure used to process the wafers will cause air from the surrounding environment to enter the processing chamber. This air will likely contain moisture and other contaminants, which, if allowed into the processing chamber, may condense on the wafer and other surfaces within the processing chamber. In the case of cryogenic aerosol processing chambers, extremely cold surfaces used to deliver or that otherwise are affected by or come in contact with the cryogenic fluid are particularly susceptible to condensation of moisture and other contaminants.
The transferring of a wafer into and out of a cryogenic aerosol processing chamber thus is typically done within a sealed handling environment that surrounds an input/output port in the chamber. A plurality of wafers to be processed are typically positioned within a separate evacuated chamber that is contained within the handling environment, and a robotic arm that is positioned in another separate evacuated chamber in the handling environment is used to remove the wafer from the processing chamber through the port, grasp a new wafer from the plurality of wafers, and insert the new wafer through the port into the processing chamber. The pressure of the handling environment is held at a lower level than the pressure at which the wafers are processed. That is, the handling environment is typically on the order of 10 to 30 milli-Torr, while the pressure of the processing chamber during cleaning is typically about 50 Torr.
In order to remove or insert a wafer into the processing chamber of such a cryogenic cleaning apparatus, then, while minimizing the introduction of moisture or other contaminants onto the wafers to be processed, the processing chamber, the chamber containing the robot, and the chamber containing the plurality of wafers must be substantially equalized at each transition of the wafer from one of these chambers. That is, not only is it desirable to prevent fluid flow into the processing chamber, it is also desirable to prevent fluid flow out of the process chamber. To do this, the processing chamber is pumped down to a pressure that is substantially equal to the pressure of the handling environment to also prevent the transfer of gas from the processing chamber into the handling environment. This is because any pressure differential between the processing chamber and the handling environment will cause the transfer of some of the environment from within the higher pressure region to the lower pressure region when the processing chamber is breached. Any such fluid flow may cause a recirculation of contaminants onto either the wafer that was just processed or onto a wafer in the handling environment that is about to be processed. So, only after the processing chamber has been pumped down to the pressure level of the handling environment can the processing chamber be breached by opening the input/output port. Then, the processed wafer can be removed, and a new wafer can be inserted into the chamber with minimal exchange of environments between the processing chamber and the handling environment. The processing chamber can then be resealed and its pressure can be raised to the desired processing pressure.
As mentioned above, it is important to control the introduction of moisture and contaminants into any environment in which the semiconductor wafers are positioned. This is particularly true where the environment in which the wafers are positioned is evacuated during a process cycle, such as during the transfer of a wafer into or out of the processing chamber described above. This is because a reduction in pressure may cause moisture and any surrounding contaminants to condense upon the wafer or cryogenic elements of the apparatus. In an aerosol processing apparatus, where apparatus components can be extremely cold due to the extremely cold temperatures at which the stream of cryogenic fluid is dispensed within the processing chamber, these problems can be particularly acute.
The step of reducing the pressure of the processing chamber from its processing pressure down to the level of the handling environment prior to breaching the processing chamber is time intensive, however, often taking 20 seconds or more to accomplish, which represents a substantial portion of the entire period of time it takes to process a wafer. This affects the number of wafers that can be processed in a given time period (i.e. the through-put of wafers through the chamber), which in turn negatively impacts the efficiency of the overall wafer manufacturing process. Moreover, it is time consuming in such prior art equipment to properly control the pressure levels of the various chambers in the handling environment and the processing chamber during wafer transfer between these chambers. Additionally, prior art equipment are complex given the need to maintain the handling environment chambers at low pressure while maintaining the processing chamber at a separate pressure. This adds cost and complexity to construction and maintenance of the overall system.